Television



June 15, 1937. F. c. P. HENROTEAU TELEVI S ION 2 Sheets-Sheet 1 FiledJan. 23, 1951 June 15, 1937. F. c. P. HENROTEAU TELEVISION Filed Jan.23, 1931 '2 Sheets-Sheet 2 Arr-ya.

Patented June 15, 1937 PATENT- OFFICE TELEVISION Francois Charles PierreHenroteau, Ottawa, 0n-

tarlo, Canada, assignor to Electronic Television Company, limited,Ottawa, Ontario, Canada Application January 23, 1931, Serial No. 510,705In Canada January 20, 1931 13 Claims.

This invention relates to television, one object being to transmiteither. by wire or by radio the moving images of scenes under ordinaryillumination and at the same time provide that the image transmitted beexceedingly sharp and well defined, showing even the smallest details.

Another object of the invention is to permit the transmission of animateor still views under ordinary daylight illumination regardless, withinlimits, of the size of these views, that is to transmit all views whichit is possible at present to photograph with a moving picture camera.

A further object of the invention is to provide a method whereby eachpoint of the scene to be 15 televised can be impressed on thephotoelectric surface for a greater time than has hitherto beenpossible.

A still further object of the invention is to provide a method wherebyall the points of the scene to be televised are simultaneously projectedon the transmitter and not successively projected thereon, as is thecase with all practical methods of television now in use.

In all methods of television used at present the scene to be televisedis divided into a number of elements according to the amount of detailrequired in the scene received. Each of these elements is thensuccessively projected on the photoelectric transmitting cell and. sentto the receiving station. My method, however, differs radically from theabove method in that all the elements of the sceneare simultaneouslyprojected on the transmitter. If, according to the above method, it isdesired to transmit an entire scene every sixteenth of a second and thescene is to be divided intoten thousand elements, then each element willbe projected on the transmitting screen for only one one-hundred andsixty thousandth of a second. It is known that the electric energyliberated by photoelectric material is proportional to the amount oflight falling on the material multiplied by the time during which thislight acts. If, therefore, the light from each element of the scene isto remain on the transmitter for only one one-hundred and sixtythousandth of a second, a very strong illumination of this scene isnecessary in order that the photoelectric material may emit enoughenergy for transmission and, for this reason, it is at presentpractically impossible to transmit scenes under ordinary daylightillumination.

According to my method, transmission is divided into three periods ofequal length, the scene being projected on the transmitter during one ofthese periods. Since all the elements of the scene are simultaneouslyprojected on the transmitter, the light from each element of the formerfalls on the latter for one third of one sixteenth of a second, that isfor almost four thousand times longer than in known methods. If,however, the number of elements into which the scene is dividedincreases, then this proportion becomes still greater. In order totransmit the scene, a very strong spot of light is caused to scan theentire surface of the transmitting screen on which the scene has beenprojected. The time for which this scanning beam will act upon oneelement of the transmitter will be ten thousand times shorter than thetime for which the light of the scene acts upon the same element.However, the light of the scanning beam can be made, on the average, tenthousand times greater than the light received from the scene.Therefore, the electric energy liberated from one element of thephotoelectric material of the transmitter will be of the same order ofmagnitude as the energy liberated by the light of the scene whichstrikes that element. Thus, assuming the same illumination of the scenein transmission by my method and transmission by all other practicalmethods, the energy available for the transmission of the scene by mymethod will be, on the average, a number of thousand times greater thanthe energy available for the transmission of the scene by all practicalmethods.

It will be seen that by the use of my method,

-daylight television is made quite possible and,

since a very large number of elements may be formed in the particulartransmitter which I use, a great wealth of detail in the transmittedscene is made possible.

The basic difference between my method of television and those now usedis the simultaneous projection of all parts of the scene on the cathode,as has already been disclosed in my U. S. Patents Nos. 1,903,112 and1,903,113. In the device as shown-in these patents, the cathode wasdivided into a multiplicity of tiny photoelectric elements insulatedfrom one another. The view being projected on this cathode raised theindividual elements thereof to different positive potentials, de--pending upon the intensity of the light which struck these elements. Thecathode was then scanned by a strong beam of light and a modulatedelectronic current was thus received by the anode. The interior of thephotoelectric cell was coated with a layer of photoelectric material. Inorder to bring the various elements of the cathode back to a uniformpotential, a strong beam of light was projected on the photoelectriccoating Just mentioned, this light being of such wave length that theelectrons which it detached from the coating had practically zerovelocity and were thus attracted to any part of the cell which was at apositive potential. The anode and the grid being grounded, they wereattracted to the cathode and neutralized the positive charges of thevarious elements thereof.

a certain part of the function of the cathode of my previous patents,namely, that of retaining an electrostatic reproduction of the view.

The regeneration of the cell is performed according to my presentinvention in a manner entirely different from that disclosed by me in myprior patents. After the picture has been sent, it is necessary to bringthe various elements of the grid back to a uniform potential. Thephotosensitive coating oi the cathode is of a material which issensitive to light in the visible spectrum but practically insensitiveto ultra-violet light, while the coating of the metallic elements of thegrid is of a material which is insensitive to visible light butsensitive to ultra-violet light. Thus in order to bring the elements ofthe grid to a uniform potential, I cause a strong beam of ultra-violetlight to be projected thereon, the

" cathode being practically unaffected by this beam. I may, ifnecessary. provide means for screening the cathode from the beam whileexposing the grid thereto.

According to my present invention, I provide a cathode in the form of aplate having a coating of photo-sensitive material thereon. An anode isalso provided within the cell, and between the anode and the cathode,very close to the latter,

is positioned a grid. This grid is formed of a large number of quartzfibres each fibre having a number of mutually insulated metallicelements thereon, the number of the fibres and the number of elements oneach fibre depending upon the degree of detail desired in the finalpicture. Mounted on a shaft is a suitable shutter for admitting thelight of. the view, the scanning beam and the ray of ultra-violet lightthrough three different lenses, respectively. Mounted on the same shaftas the shutter are suitable commutators for effecting the variouselectrical connections necessary for the anode and cathode.

The transmission of a picture is divided into three different stageswhich may be briefly described as follows:-

(A) The cathode and anode are connected to a source of comparativelyhigh negative potential, of equalvalue for both, so that the grid, whichhas no electrical connection, will be at a potential near zero andtherefore positive with respect to the rest of the elements in the cell.At the same time theiimageof'a'. view 'is projected on the cathode.Different parts of the photo-sensitive coating of -this cathode willemit different numbers'of 'electronsdepending upon the degree ofintensity of the light of the particular part of the view which strikesthem. These electrons will be collected by the elements of the gridadjacent to the parts of the cathode from which they were emitted andthese elements will thus attain varying degrees of negative potential,corresponding ductive elements i 2.

to the degree of intensity of the light which struck the adjacent partsof the cathode. In this manner an electrostatic reproduction of the viewwill be formed on the grid.

(B) The view is then interrupted and the cathode grounded, while theanode is connected to a source of comparatively high positive potentialand to the grid of the first thermionic valve of a transmitter. At thesame time a very strong beam of light from a cathode ray oscillograph iscaused to scan the photo-sensitive surface of the cathode. The electronsemitted under the influence of this beam will be attracted to the anodeby reason of its positive potential but their number in each instancewill be controlled by the potential of the particular element of thegrid adjacent to which they must pass. A modulated potential will thusbe impressed on the grid of the first thermionic valve of thetransmitter, and this potential will be proportioned in intensity to theintensity of the light of the various portions of the view which wereoriginally projected on the cathode.

(C) The scanning beam is interrupted, the

cathode and anode are grounded and a strong beam of ultra-violet lightis projected on the grid. Under the influence of this light, themetallic elements of the grid, which are composed of a metal, such aszinc, sensitive to ultraviolet light, will emit electrons until all theelements reach a uniform potential which will be very nearly zero. Theemitted electronswill be captured by the cathode or by the anode.

The invention will be more fully understood by reference to the attacheddrawings in which:

Figure 1 is a general view of my apparatus partly in section.

Figure 2 is a plan view of the grid. Figure 3 is a plan view of theshutter showing the relation of the various lenses thereto, and

Figure 4 is a view showing a modification of the apparatus used forregenerating the grid.

In the drawings, l is a photoelectric cell which is formed with aflattened part 2 having a quartz window 3 therein and two lenses 4 and 5mounted adjacent thereto, the centres of the two lenses and that of thequartz window being at the aploes of an equilateral triangle, as shownin Fig. 3. The part 2 is opaque except for the quartz window 3 and theparts directly behind the lenses 4 and 5. Mounted within the tube is ananode 6 and a screen 1 constituting a cathode and being formed of anelectro-conductive plate 1a having thereon a layer 8 of material such ascaesium sensitive to visible light but practically insensitive toultraviolet light. This layer is preferably monomolecular, since it iswell known that this enhances the photoelectric activity.

The anode 6 is made in the form of a small sphere partly to prevent itsinterfering with the various beams of light through the lenses 3, 4, and5 and partly to reduce its electrical capacity.

Mounted between the anode 6 and cathode I and very near the latter is agrid 9. This grid consists of a large number of quartz fibres llstretched between posts ii and having thereon a multiplicity of mutuallyinsulated electro-con- The elements of the grid are formed by silverplating an extremely thin quartz fibre, then electroplating theplatedfibre with a metal, such as zinc, which, while insensitive tovisible light is sensitive to ultra-violet light, and finally removingthe entire metal plating from the quartz at regular intervals. by

some suitable process, such as dissolution, so that cent elements by ashort length of bare quartz.

, The metallic elements-of the adjacent wires are preferably staggeredwith respect to one another, that is, the elements of one wire willoccupy the 1, 3, 5 positions while the elements of the next wire willoccupy the 2, 4, 6 positions.

A shutter I3, arranged opposite the flattened part 2 of the cell, has anopening I4 therein of such size that it will not uncover more than onetransparent portion of the part 2 atone time. The shutter I3 is mountedon a shaft I5 and rotates therewith. Mounted on the same shaft androtating therewith is a commutator I6 of insulating material having ametallic sector II thereon, this sector being connected to the anode 6by means of a wire I8. Arranged around the commutator are three contactsI9, 20, and 2I, the contact I9 being connected to ground 22, the contact20 being connected through negative battery 23 to ground 24 and thecontact 2I being connected through resistance 25 and positive battery 26to ground 21 and also to the grid 28 25 of the first thermionic valve 29of a transmitter.

The contacts I9, 20 and 2| are arranged around thecommutator at theapices of an equilateral triangle and the angle subtended by the arc ofthe metallic sector I! is slightly less than 120 30 so that this sectorconnects-with only one contact at a time. A commutator 30 similar to thecommutator I6 and having a metallic sector 3I similar to the metallicsector I1 is also mounted on the shaft I5, the sector 3| being connectedto the cathode by a wire 32. Arranged around the commutator are threecontacts 33, 34 and 35, the first being connected to ground 36, thesecond through negative battery 31 to ground 38 and the third to ground39.

A cathode ray oscillograph '40 for scanning purposes is arranged in sucha way that the light produced by the impact of its electronic stream onthe fluorescent screen M will pass through the lens 5 and that itsfluorescent screen M will be a conjugate plate to the cathode I withrespect to this lens. In the embodiment shown the cathode rayoscillograph is arranged above the apparatus and its light is reflectedby the mirror 42. If desired some other form of scanning means 50 mightbe used, the cathode ray oscillographhaving been shownmerely by Way ofexample and because it is thought to be the most suitable.

In Figure 1 the device for producing the ultraviolet light is shown byway of example as comprising an arc light 43 having in front thereof apiece of Jena glass 44 which will allow only the ultra-violet part ofthe light from the arc to pass.

Although the material with which the cathode is coated is practicallyinsensitive to ultra-violet, it may be advisable to arrange theapparatus in such a manner that the ultra-violet light for regeneratingthe grid will be prevented from striking the cathode coating. Thisarrangement is illustrated in Fig. 4, in which only those parts directlyrelevant to it are shown.

What would correspond to a negative photographic reproduction of thegrid 9 is formed on a plate 45 transparent to ultra-violet light so thatthis light may only traverse the plate at those points which correspondto the wires of the grid. In the drawings the black lines 46 representthe parts of the plate which correspond to the inter-wire spaces of thegrid and are opaque 75 to ultra-violet light, while the white lines 41repsensitive surface 8 of the cathode.

resent the parts of the plate which correspond to the wires of the gridand are transparent to ultra-violet light. The reproduction of the gridon the plate may.,be performed in any suitable manner, eitherphotographically or otherwise. The finished plate is placed in such aposition that it will form a conjugate plane to the grid 9 with respectto a quartz lens 48 which is used in this case instead of the quartzwindow 3. The

source of ultra-violet light is positioned so that The whole apparatuswill be suitably magneti- 4 cally and electrically shielded.

The operation of the apparatus which has been described above is asfollows:

Transmission takes place in three stages, each stage lastingapproximately 1/50 of a second:

(A) The shaft I5 in its rotation connects the anode 6 through wire I8,sector I! and contact 20 to negative battery 23, this battery having acomparatively high potential, such as minus 100 volts. At the same timethe cathode 1 is connected through wire 32, sector 3I and contact 34 tonegative battery 31, this battery having the same potential as battery23. Owing to the rotation of the shaft, the opening I4 of the shutter I3is at this instant brought into registry with the lens 4 and the imageof a view is projected through the opening and the lens onto the photo-Since both the cathode and the anode are at the same comparatively highnegative potential and the grid is unconnected, the metallic elements ofthe latter are, therefore, positive with respect to the rest of theelements of the tube.

Under the influence of the light from the-view different parts of thecathode will emit diiferent numbers of electrons, depending upon theintensity of the light in the particular part of the view which isstriking them. All the electrons emitted from any one point on thecathode will be collected by the nearest element I2 of the grid, whichelement will thus assume a certain negative potential. Owing to thesmall size of the elements and therefore their very low capacity, thenegative potentials which they assume will be comparatively high evenfor the very small electronic emission which they receive. Each elementof the grid receiving a difierent number of electrons will be raised toa difierent negative potential. It will thus be seen that the light ofthe view striking the cathode will produce an electrostatic reproductionof this view on the grid.

(B) The light from the view is interrupted and the rotation of the shaftI5 brings the opening I4 of the shutter I3 into registry with the lens5. At the same time it connects the anode through the sector I! andcontact 2I to the positive battery 26 and to the grid 28 of the firstthermionic valve 29 of a transmitter and also connects the cathodethrough the sector 3| and contact 35 to ground 39. While the lens 5 isin registry with the opening I4 of the shutter I3, the beam of lightfrom the cathode ray oscillograph 40 scans the photo-sensitive surface 8of the cathode "I. The scanning beam of the cathode ray oscillograph isextremely strong and of constant intensity so that under its influencethe same number of electrons will be detached from each successive pointof the cathode which it strikes and attracted to the anode by reason ofthe comparatively high positive potential of the latter. One of themetallic elements I2 of the grid 9 will,

negative potentials of the different metallic elements of the grid, sothat, in the result, the anode will receive an electroniccurrentmodulated in accordance with the intensityof the light of thedifferent parts of the view which was originally projected on thecathode. The modulated electronic current received by the anode willmodulateits potential and these potential modulations will be impressedon the grid 28 of the first thermionic valve 28 of the transmitter. Fromhere transmission is by known methods.

It will be noticed, in connection with this operation, that the anode,being in the form of a small sphere, has a very low electric capacityand.

that its electrical connection to the grid 28 of the thermionic valve ismade as short as possible in order to reduce the capacity of thisconnection also. Thus, in operation, the small variations of electroniccurrent received by the anode will cause quite appreciable variations inits potential and thus cause the same variations of potential on thegrid of the thermionic tube of the trans- 30 mltter.

(0) The rotation of the-shaft ls moves the opening ll of the shutter ll.into registry with the quartz window 3 and at the same time groundsboth the anode and cathode at grounds 22 and 3 6 respectively. Theultra-violet light transmitted through the Jena glass will pass throughthe quartz window 8 and strike the metallic elements I 2 of the grid 9.It will also strike the photosensitive coating 8 of the cathode butsince this coating is almost completely insensitive to ultravioletlight, the latter will have no effect on it. The zinc coating of themetallic elements II of the grid 9, however, being photo-sensitive toultra-violet light, will emit electrons, which will be attracted by thecathode and also by the anode, since both these electrodes are groundedand therefore positive with respect to the various elements of the gridwhich are at various negative potentials. As soon as an element of thegrid has emitted enough electrons to acquire a slight positive potentialthen any further electrons which it emits will be reattracted to it andit will retain the same potential. In this manner all the elements ofthe grid will be brought to a uniform potential which will be slightlypositive.

If the regenerating arrangement shown in Figure 4 is used the operationis only slightly modified. When the opening I of the shutter l8registers with the quartz lens 48, the ultra-violet light, which haspassed through the screen 45 and'has been reflected by the mirror 49,passes through the lens 48 and strikes the wires of the grid 9. Owing tothe construction of the screen 'the light is prevented from striking thecathode. The elements of the grid are brought to a uniform potential asdescribed above.

Immediately after this last operation is completed the cycle ofoperations A, B, C is repeated many times. In each case operation Cbrings the metallic elements of the grid to the same uniform potential.v

' The irequency'band necessary for transmission might be narrowed if,instead of using only one apparatus where the whole cycle of operationsis completed in one sixteenth of a second, three on the receiver.

-- thereof.

aosspos apparatuses were used. In this case while the first apparatuswas performing operation 'A the second would be performing operation Band the third, operation C. Thus, though a picture would be transmittedevery 1" second, each operation could last instead of only 1/50 of asecond. This would be of importance in transmitting the picture sincethis operation could then be spread over three times the period whichcould be allowed when only one apparatus was used and the frequency bandfor transmission thus narrowed.

Very strong, enlarged and contrasted images of very faint, still objectscould be produced with my system owing to electrical amplification. Theshutter I3 would be brought to a position to allow the view to fall onscreen 8 for a suitable length of time. The shutter would then berotated to a position to allow scanning of the screen and this scanningcould be repeated without any intermediate operation for as long asdesired since the electrostatic image of the object would always remainon the grid. My device could for instance be attached .to a powerfulastronomical telescope and, while the image focussed would be large andweak, a very vivid strong image would appear The device could also beattached to a microscope andpermit hitherto invisible objects to beseen.

The effect produced by the scanning beam'of the cathode ray oscillographmay be achieved in a modification of my invention by anotherarrangement.

In this modification, the cathode is formed of a an extremely thin plateof aluminium or berylium, the latter being preferred owing to its lowdensity. This plate is coated on one side with a monomolecular layer ofphoto-sensitive material such as caesium, this side of the plate facingtoward the grid. The plate itself forms the screen of a cathode rayoscillograph, the electronic stream of the latter being directed againstthe uncoated side of the plate, namely that facing away from the grid.

At the appropriate time for the scanning operation the cathode rayoscillograph comes into operation to cause an electronic stream to scanthe uncoated side of the plate. The electrons in this stream are movingat an extremely high speed and will pass through the plate. In so doing,however, their speed will be considerably reduced so that after theirpassage they will be moving with approximately the same speed as theelectrons emitted from the photo-sensitive surface 8 as described inconnection with Figure 1. The berylium plate, being of uniform thinnessand density, the speed of the electronic stream, after its passagetherethrough, will be uniform for all points. After they have passedthrough the plate the electrons will be attracted by-the anode, thenumber reaching the latter from any point of the cathode beingcontrolled in each instance by the potential of the metallic element ofthe grid near which they must pass.

.Thus the same result will be produced by this arrangement as would beproduced by the scanning arrangement disclosed above.

' Various modifications might be made in the apparatus disclosed forcarrying out my invention without departing from the spirit or scopeThus for instance, it is not necessary that the shutter l8 andcommutators l8 and ll be all mountedon the same shaft, this particulararrangement having been disclosed merely because it was thought to bethe most convenient. 7

quence, causing said stream to be modulated by said electrostaticreproduction, and picking up the modulated stream at an anode.

2. A method or electrical image transmission 15 which comprisesimpressing an image upon a photosensitive surface, collecting theelectronic emission from said surface to form an electrostaticreproduction of said image on means other than said surface, causing anelectronic stream 20 to be emitted from every point of said surface insequence, causing said stream to be modulated by said electrostaticreproduction, picking up the modulated stream at an anode, and finallycausing said electrostatic reproduction to disappear.

3. A method of electrical image transmission which comprises impressingan image upon a uniformly electro-conductive and uniformlyphotosensitive surface, collecting the electronic emission from saidsurface to form an, electro- 30 static reproduction of said image onmeans distinct from said surface, causing an electronic stream to beemitted from every point of said surface in sequence, causing saidstream to be modulated by said electrostatic reproduction and 35 causingthe modulated stream to be attracted by an anode.

4. A method of electrical image transmission which comprises impressingan image upon a surface photosensitive only to visible light, collectingthe electronic emission from the said surface to form an electrostaticreproduction of said image on means distinct from said surface andphotosensitive only to ultraviolet light, causing an electronic streamto be emitted from every point of said surface in sequence, causing saidstream to be modulated by said electrostatic reproduction, picking upthe modulated stream at an anode, and finally causing said electrostaticreproduction to disappear by means of ultraviolet light.

5. Apparatus for the electrical transmission of images comprising acell, a photosensitive surface within said cell, means for impressing animage on said surface, separate means in the form of a grid also withinsaid cell, formed with a multiplicity of mutually insulatedelectroconductive elements, for retaining an electrostatic reproductionof said image, means for thereafter causing said photosensitive surfaceto emit an electronic stream from every point thereof in sequence, andan anode for receiving said electronic stream modulated by saidelectrostatic reproduction.

6. Apparatus for the electrical. transmission of images comprising acell, a photosensitive surface within said cell, means for impressing animage on said surface, separate means in the form of a grid also withinsaid cell, composed of a number of'insulating fibres each having anumber of mutually insulated electroconductive elements thereon, forretaining an electrostatic reproduction of said image, scanning meansfor causing said photosensitive surface to emit an electronic streamfrom every point thereof in sequence, and an anode for receiving'saidelectronic stream modulated by said electrostatic reproduction.

7. Apparatus for the electrical transmission of images comprising acell, a surface within said cell, photosensitive only to visible light,means for impressing an image on said surface, a grid also within saidcell formed witha multiplicity of mutually insulated electro-conductiveelements, said elements being photo-sensitive only to ultra-violentlight, said grid serving to retain an electrostatic reproduction of saidimage, means for causing said photosensitive surface to emit anelectronic stream from every point thereof in sequence, and means forthereafter projecting ultraviolet light on said grid to neutralize saidelectrostatic image.

8. Apparatus for the electrical transmission of images comprising acell, a photosensitive surface within said cell, a grid also within saidcell composed of a multiplicity of mutually insulated electroconductiveelements, said elements being sensitive only to light of a differentwave length from that to which said surface is sensitive, means forimpressing an image on said surface, means for causing the elements ofsaid grid to collect the resulting electronic emission from the adjacentportions of said surface and thus assume various negative potentials,means for scanning said surface with a beam of light, and means forcausing another electrode in said cell to attract the resultingelectronic stream, the electroconductive elements of said grid servingto modulate the last mentioned electronic stream.

9. Apparatus for the electrical transmission of images comprising acell, a surface within said cell, photosensitive only to visible light,means for impressing an image on said surface, a grid also .within saidcell formed with a multiplicity of mutually insulated electroconductiveelements, said elements being photo-sensitive only to ultraviolet light,said grid serving to retain an electrostatic reproduction of said image,means for cause ing said photosensitive surface to emit an electronicstream from every point thereof in sequence, means for thereafterprojecting ultraviolet light on said grid to neutralize saidelectrostatic image, and means for shielding said photosensitive surfacefrom said ultraviolet light.

10. Apparatus for the electrical transmission of images, comprising acell, a photosensitive surface within said cell, means for causing anelectronic stream to be emitted from every point of said surface insequence, means for impressing an image on said surface, separate meansin said cell for retaining an electrostatic reproduction of said imageand for modulating the emitted electronic stream in accordance with theelectrostatic reproduction, and an anode for receiving the modulatedstream.

11. Apparatus for the electrical transmission of images, comprisingacell, a photosensitive surface within said cell, means for causing anelectronic stream to be emitted from every point of said surface insequence, means for impressing an image on said surface, separate meansin said cell for retaining an electrostatic reproduction of said imageand for modulating the emitted electronic stream in accordance with theelectrostatic reproduction, an anode for receiving the modulated stream,and means for causing the electrostatic reproduction to disappear.

12. In a method of electrical image transmission the steps whichcomprise impressing an image upon a photosensitive surface, collectingthe electronic emission from said surface on means comprising amultiplicity oi! mutually insulated e1ectroconductive elements, to forman electrostatic reproduction 01' said image thereon, scanning a surfaceto cause an electronic current of substantialiy constant intensity to beemitted from areas of said surface successively scanned, modulating saidelectronic current by said electrostatic reproduction, picking up themodulated current at an anode, and controlling the operation '01 a 10transmitting device in accordance with the successive changes in valueof said modulated current.

13. In apparatus for the electrical transmission of images, means forscanning a screen to cause an electronic stream to be emitted therefrom.means separate and distinct from said screen tor modulating theelectronic stream in accordance .with the intensity of thedight 0! animage, and

an anode for picking up the modulated stream.

FRANCOIS CHARLES HEHRO'IIAU. l0

